1. Field of the Invention
The present invention is directed to a circuit breaker with a magnet fixing means, and more particularly, to a circuit breaker with a magnet fixing means for fixing a magnet used to break an overcurrent that occurs.
2. Description of the Related Art
In general, a circuit breaker is an electrical device provided within a distribution switchboard having a low voltage circuit (15-30 A) with AC 110/220V to be used for the purpose of preventing electric shock on human body, a fire caused by a short circuit, an accident due to an overcurrent and a short circuit, and the like.
Such a circuit breaker, as a device for sensing a fault current when the fault current and short-circuit current occur and breaking a line to protect the load and line connected thereto, is widely used in the related art instead of one combined with a knife switch and a fuse since it is small-sized and safely manipulated as well as has no trouble in inserting a fuse.
The fault current sensing function of the circuit breaker may include an overcurrent protection function and an instantaneous current protection function, and the overcurrent protection function performs a trip operation using a heater and a bimetal provided within the breaker by allowing the bimetal to be bent, and the instantaneous current protection function performs a trip operation using a magnet magnetized by an instantaneously generated high current.
According to the use of a circuit breaker, the size and conduction time of current is variably set at which a trip operation should be carried out, and in case of a thermal electronic circuit breaker having the foregoing structure, it is set not to perform a trip operation when the current flows below 105% of rated current, but set to perform a trip operation above 130% of rated current. Furthermore, when the current flows above 105% and below 130%, a time for starting the trip operation is individually set according to the size of current.
FIG. 1 is a cross-sectional view illustrating the internal structure of a typical circuit breaker. Referring to FIG. 1, the foregoing bimetal 10, heater 11, and magnet 12 are fastened by one fixing bolt. The heater 11 generates heat due to its induced current, and the generated heat is conducted into the bimetal 10. When an overcurrent flows, enough heat to deform the bimetal 10 is generated, thereby breaking the conduction of the overcurrent. Meanwhile, in describing the instantaneous current protection function, when a current above the reference current instantaneously flows, the magnet 12 is magnetized to pull an armature bar 13 disposed at the right side (with respect to FIG. 1) of the magnet 12 to the side of the magnet 12 to perform a trip operation.
In the foregoing structure, heat generated by the heater while an overcurrent flows is conducted to the side of the magnet along the fixing bolt as well as the bimetal. Due to this, an amount of heat conducted to the bimetal is reduced, thereby causing a problem that the operation of the bimetal is inaccurate. Due to this, an amount of heat transferred to the side of the bimetal should be taken into consideration during the design of a circuit breaker, thereby causing a problem that the design of the circuit breaker becomes difficult. Furthermore, the amount of conducted heat varies according to the abrasion degree of the fixing bolt and the difference of the fastening force, and as a result, there exists a problem that the operational characteristics of the circuit breaker become inconsistent.